moves Cli and Command class from network to netcmd module
moves Cli and Command class from network to netcmd module

This restructure moves the Cli object to netcmd and includes a roll up
of inor bugfix updates to CommandRunner

* CommandRunner now only allows one instance of a command in the stack and
  raise an exception if a duplidate command is detected
* CommandRunner now caches returns based on command and output
* CommandRunner is not responsible for creating Command instances

thaim/ansible,thaim/ansible